Illusion - Worthless. Nothing in this tree is useful and even if it was slightly useful each skill is trumped by potions and items you find along your journeys.

Conjuration - Underpowered compared to all melee trees and your own companion. You already have a near indestructible companion at your beckon call. You can choose to forgo your companion so you can be forced to summon and blow your magika every fight but that seems more like a chore.

If you get every dual wielding perk ... You can 1-2 shot everything. That also without the best weapons.

I have to start by saying that I loved this game. No other game I ever played gave me the feeling of immersion like this one. The problem though is that like many others, I took certain skills that ruined the game for me and made progressing completely worthless. No one has fun in an RPG when 100% of all looted items have become useless and taking down the toughest creatures in the game takes a few seconds. The problem like many of you already know is the skill and perk system. The disparity between the skill trees is glaring. Some perks and trees are so good that if you choose them you will ruin your game experience while others are so bad that if you choose them you will 100% waste those points. This results in 95% of us ending up with an incredibly overpowered or underpowered character by level 30.

One-handed - Balanced. Dual weilding 1 handers is pretty useless becuase of the lack of block ability and the negligible damage increase. Otherwise Sword/Shield, Sword/Spell is a fun combination.
Light armor - Unless you are a primary caster it's worthless. Run speed has little to no noticeable difference, it's not lighter when you get the perk to make Heavy Armor weightless, not much difference for stealthing.
Sneak - Completely overpowered. 100% camo was overpowered in Oblivion the same for Sneak in this game. 1 shotting pretty much anything from stealth with a bow or dagger gets old quick. Oh yeah choosing Shadow Warrior may as well bring up the ending credits.
Alteration - Balanced as long as you get the perk to have unlimited duration time on your spells. Otherwise get very used to pausing your gameplay every 15 seconds to bring up the menu to cast a buff on yourself.
Smithing - Completely overpowered. For the low low cost of a few hundred iron daggers, you too can completely ruin the fun of looting, dungeon exploring, or quest rewards.
Block - One of the few balanced skills in the game. It requires timing to use which increases the user experience and is useful to use often.
Heavy Armor - Simply better than light armor in almost every situation even for Sneaks
Lockpicking - Worthless if you get the skeleton key. Still worthless otherwise if you have enough lockpicks and common sense.
Enchanting - The most overpowered of all the skills. Not only does it make finding items completely useless, but selling off enchanted iron daggers (which pretty much everyone figures out) breaks the fun of selling items for gold.
Alchemy - Overpowered. What's with the crafting in this game? At first it may not seem overpowered but at some point you will quickly realize that you can't ever die when you are holding 100 health pots, magic pots, and +dmg pots. Also 50g to make a pot and 500g sell back gets ridiculous.
Two-Handed - Balanced. Even though giving up the shield is huge in Skyrim, you aren't gimping yourself by choosing 2 hander. It's not over the top or underpowered.
Speech - Worthless. Gold becomes trivial by the time you can invest in this tree. Persuasion and Intimidate has little to no impact on a story line.
Pickpocket - Worthless. Either you pickpocket early with an extremely low chance of success of getting anything valuable or you wait for pickpocket items/potions and realize by that point of the game the items are useless.
Archery - Overpowered. It's terrible that no matter how you spec you will end up using a bow and arrow. Used from stealth and it's over the top. I just can't see Gandolf chasing a dragon around on foot with a bow and arrow.
Illusion - Worthless. Nothing in this tree is useful and even if it was slightly useful each skill is trumped by potions and items you find along your journeys.
Conjuration - Underpowered compared to all melee trees and your own companion. You already have a near indestructible companion at your beckon call. You can choose to forgo your companion so you can be forced to summon and blow your magika every fight but that seems more like a chore.
Destruction - Underpowered compared to all melee trees. If you aren't comparing then Destruction becomes a challenging tree that requires time and patience to kill each enemy you come across.
Restoration - Balanced unless you take up Alchemy. Then it becomes pretty useless. Instant full heal from Alchemy > Channeled heal from Resto

So in order to still experience the fun of having a decent battle and enjoy the item rewards you pretty much have to avoid the overpowered Sneak, Smithing, Enchanting, Alchemy, Archery. If you want to avoid placing your points in completely useless and/or redundant skill trees you have to avoid Lockpicking, Speech, Pickpocket, Illusion. This results in having to avoid 9 out of the 18 skills just to have that feeling you had in those first amazing 10 hours of Skyrim. The only problem is that you know you are avoiding these skills and it creates a situation even worse than the tempting option of using the difficulty slider. It creates a game where one wrong decision early in the game on skill placement results in the game not feeling genuine or fun after only 30 or so hours of gameplay.

But...but, free training is a bad thing - Am I the only one seeing this!?

Tell it to a thief... I want to see the reply.

Sigh, you have to use exploits to make things OP. I set out to make a powerful warrior, this included smithing and enchanting. I haven't boosted either with potions or enchantments, and I got what I wanted: a powerful warrior. But I'm not invincible, not by any stretch of the imagination. And FYI, dual wield gives you a massive damage boost.

I have played nearly 300 hours and many characters. My take on some of the skill trees differs from some of your own, OP.

In a general sense, naming the biggest flaw in Skyrim’s perks system is a tossup for me.

First it sets an expectation that the higher a perk is on the tree the more useful it will be. This is not always so because many of the top end abilities are low percentage based occurrences and some of the mid-range level abilities seem to be less than useful filler.

Secondly in order to flesh out the perk trees for skills you actually like to use, often times you will have to level up a skill you do not enjoy or ever want to make regular use of. It can make playing feel like a chore.

Third, the synergy between crafting skills can create exploit grade abuses of nearly any skill or game ability. I would contend that these skills should be rethought for better play.

So, here is my take on each skill tree.

One Handed: Most useful attack skill due to versatility. You can use a shield, spell, or second weapon in the off hand. Dual weapon wield was “most” useful for sneak based melee characters.

Two Handed: Slow with a big hit. You’ll need to use cover mid-levels to get close to mage like enemies in mini packs.

Block: Very nice advantages on the left side of the tree and the top ability. Disarming bash sounds nice until you realize it is only effective 10 -20% of the time. Power bash viability is linked to your stamina as it will be shared with your weapon skill…

Heavy Armor: Most useful for less staminia reliant and non-shield using builds and takes the a couple more perks to fully make use of. You can easily hit armor cap with either armor skill.

Light Armor: Most useful for stamina intensive or sneak use intensive builds. You can easily hit armor cap with either armor skill.

Archery: Well balanced on its own. With sneak you’re a very effective one shot sniper. Add in crafting and you can become an invisible, long range, death canon.

Lockpicking: Five points here can be extremely useful “IF” you do not want to rely heavily on selling items to merchants for gold or crafting for enchanted armor or weapons and would rather find them. Otherwise, it’s a questionable perk tree to invest in.

Sneak: Frustrating early on but becomes incredibly useful at the high end with some choice perks. Its play enjoyment depends on your degree of patience.

Pickpocketing: It’s hard to justify spending perks points here but even without them this skill can be incredibly useful for what amounts to free training in most any skill up to 50 points. Most all NPCs do not carry much coin. They have the occasional valuable you can nab to sell for coin if you have a fence.

Speech: Perhaps the game’s least useful skill. Maybe if you just want to RP a wealthy merchant or noble but it has so little actual game use that it can only be looked at as a waste. Levels easily by way of training or natural use in selling “tons” of items… Item value seems to have some effect. You might could make it OP with some enchantig. *cough*

Alteration: A high value perk tree with good returns. The spells are very useful from low level to high. Paralysis often seems more combat useful than most destruction spells. Add in damage reduction…

Conjuration: Very cool in concept but only mediocre in play until you top end the perks. In that sense it might be the most balanced tree in the game. lol

Destruction: The least punch of any combat skill and feels like support ability rather than a primary means of offense. It’s more of a mid-range softner with some AOE potential. However, AOE is of limited value as there are rarely big mobs.

Restoration: It’s the one school where I really feel the perks can be more useful than the actual spells.

Illusion: The most perk intensive skill and tree in the game to maintain usefulness for while leveling. For the cost, it can be fun and allow some cool gimmick options but it’s more practical and perk cheaper to just arrow an opponent in the knee. Take dual casting…

Alchemy: Frustrating to level and useless early game. You can buy or find better. However, it becomes very useful at the top end of the skill value and perk tree. A long term investment with big payoffs.

Enchantment: Simple to use and level. It becomes inordinately powerful and useful to any character with time. Perhaps the best perk investment to return value tree in the game.

Smithing: A must for any character relying on physical weapons and armor. Even if you don’t want to craft your own gear its valuable for improving what you have. Easy and cheap to level.

Sigh, you have to use exploits to make things OP.

Light armor - Unless you are a primary caster it's worthless.

Well done.